Since i don't want to restrict players in any way and still want some rules there will be central authority, let's call it King's City. It will be responsible for:
- protect new players' and offline players' major cities - for a price of course
- provide place for global market, where you can put your shops and also buy from other players' shops
- create basic offer and demand for common resources (although not so friendly prices)
- enforcing of peace treaties and solving territorial problems
In the end, the battle of King's City can be the ultimate challenge...